This invention relates to heat exchangers, and in particular, to heat exchangers involving gas/liquid, two-phase flow, such as in evaporators or condensers.
In heat exchangers involving two-phase, gas/liquid fluids, flow distribution inside the heat exchanger is a major problem when the two-phase flow passes through multiple channels which are all connected to common inlet and outlet manifolds, the gas and liquid have a tendency to flow through different channels at different rates due to the differential momentum and the changes in flow direction inside the heat exchanger. This causes uneven flow distribution for both the gas and the liquid, and this in turn directly affects the heat transfer performance, especially in the area close to the outlet where the liquid mass proportion is usually quite low. Any maldistribution of the liquid results in dry-out zones or hot zones. Also, if the liquid-rich areas or channels cannot evaporate all of the liquid, some of the liquid can exit from the heat exchanger. This often has deleterious effects on the system in which the heat exchanger is used. For example, in a refrigerant evaporator system, liquid exiting from the evaporator causes the flow control or expansion valve to close reducing the refrigerant mass flow. This reduces the total heat transfer of the evaporator.
In conventional designs for evaporators and condensers, the two-phase flow enters the inlet manifold in a direction usually perpendicular to the main heat transfer channels. Because the gas has much lower momentum, it is easier for it to change direction and pass through the first few channels, but the liquid tends to keep travelling to the end of the manifold due to its higher momentum. As a result, the last few channels usually have much higher liquid flow rates and lower gas flow rates than the first one. Several methods have been tried in the past to even out the flow distribution in evaporators. One of these is the use of an apertured inlet manifold as shown in U.S. Pat. No. 3,976,128 issued to Patel et al. Another approach is to divide the evaporator up into zones or smaller groupings of the flow channels connected together in series, such as is shown in U.S. Pat. No. 4,274,482 issued to Noriaki Sonoda. While these approaches tend to help a bit, the flow distribution is still not ideal and inefficient hot zones still result.
In the present invention, barriers or partitions are used in the inlet manifold to divide the heat exchanger into sections. The barriers have orifices to allow a predetermined proportion of the flow to pass through to subsequent sections, so that the flow in the sequential sections is maintained in parallel and more evenly distributed.
According to the invention, there is provided a heat exchanger comprising a first plurality of stacked, tube-like members having respective inlet and outlet distal end portions defining respective of inlet and outlet openings. All of the inlet openings are joined together so that the inlet distal end portions form a first inlet manifold, and all of the outlet openings are joined together so that the outlet distal end portions form a first outlet manifold. A second plurality of stacked, tube-like members is located adjacent to the first plurality of tube-like members. The second plurality of tube-like members also has inlet and outlet distal end portions defining respective inlet and outlet openings. All of the inlet openings are joined together so that the inlet distal end portions form a second inlet manifold and all of the outlet openings are joined together so that the outlet distal end portions form a second outlet manifolds. The second outlet manifold is joined to communicate with the first outlet manifold. The second inlet manifold is joined to communicate with the first inlet manifold. A barrier is located between the first and second inlet manifolds. The barrier defines an orifice to permit the portion only of the flow in the first inlet manifold to pass into the second inlet manifold.